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All About Continuous Glucose Monitors for People with Diabetes

Glucose Monitoring

Diabetes is a serious and growing problem in the United States. According to the Centers for Disease Control & Prevention, approximately 30.3 million Americans have diabetes, or about one in 10 people. That’s up from about 26 million people in 2010.

Also known as hyperglycemia, diabetes is a broad term for a condition that causes the body’s blood glucose (sugar) levels to rise higher than normal. In many cases, it can be effectively managed through diet, exercise, medication, and blood glucose monitoring. As a supplement to the traditional finger-prick technology that people with diabetes have relied upon for many years to check their blood glucose levels, continuous glucose monitors (CGMs) offer a more convenient and less painful way for people to track their blood sugar and make positive lifestyle choices.

November is national Diabetes Awareness Month, so UAB Medicine prepared this article to explain CGMs, including information on how they work, their benefits, and where to obtain one.

What Are CGMs?

In September 2017, the U.S. Food & Drug Administration approved the first continuous glucose monitoring system for use by adults with diabetes. This technology offers an alternative to taking blood from the fingertips, where the sample is taken from tiny blood vessels called capillaries. According to Alison Wharton, MPH, RDN, CDE, LD, a diabetes and nutrition education specialist with UAB Medicine, CGMs track blood sugar levels 24 hours per day by measuring the amount of glucose in interstitial fluid, which is the fluid that surrounds blood vessels.

Continuous glucose monitoring has proven to be effective for people with type 1 diabetes who use an insulin pump to manage blood sugar fluctuations. Type 1 diabetes means that the person’s body does not produce insulin, which is necessary for regulating blood sugar levels. However, some doctors and researchers believe that CGMs also may be helpful for people who have type 2 diabetes, meaning that their bodies don’t respond properly to insulin. These monitors could even be useful in helping individuals diagnosed with pre-diabetes improve their lifestyle habits based on CGM readings.

How CGMs Work

Instead of requiring users to prick their fingertips as many as 7-10 times per day, CGMs utilize a tiny sensor wire that the user inserts below the surface of the skin and secures with an adhesive patch. The sensor usually is worn on the abdomen or the back of the arm, and it monitors the person’s glucose levels throughout the day and night. The readings taken by the sensor are transmitted to a handheld electronic monitor or smartphone, where real-time data is provided to users about their glucose levels. Current models can be worn for 7-14 days, and some are only recommended for use by people age 18 and older.

Benefits of CGMs

Since CGMs continually collect blood sugar data, they can help identify issues and patterns that traditional finger-prick technology cannot. For example, CGMs can record low blood sugar levels while a person is sleeping, track spikes between meals and in the early morning, evaluate diet changes, and provide insight about how medications and exercise regimens are impacting the body. The devices also make it easier for a patient’s health care provider to adjust treatment plans.

“CGMs, when used appropriately, provide daily, continuous guidance on how to adjust therapy to more consistently keep blood sugars within the target range and avoid prolonged, severe highs and lows,” Wharton says.

Accuracy of CGMs

The accuracy of CGMs varies and is measured by mean absolute relative difference (MARD). This accuracy measurement is not a precise value but more of an indication and reference point, since MARD does not take into account the frequency of measurements. However, CGMs with a MARD of less than 10 is considered to be good, and all new FDA-approved CGMs achieve this level of accuracy. The results generated by CGMs are interpreted differently than those produced by traditional finger-prick technology because CGMs measure the glucose levels in interstitial fluid rather than glucose levels in the capillaries within the fingertips. Also, the lag time between actual blood sugar levels and CGM values may contribute to minor discrepancies.

“The lag gap continues to improve with improved technology,” Wharton says. “Individuals should be reminded to look more at glucose trending than snapshots of blood sugars.”

As promising as CGM technology is, it doesn’t entirely replace finger-prick technology, Wharton says. “Sometimes the CGM device will require you to check with your traditional meter, too, but it greatly reduces the need for frequent finger stick checks,” she says.

While some CGMs still require calibration using a reading obtained with finger-prick technology, finger sticks generally shouldn’t be required more than twice a day if the CGM is calibrated correctly, Wharton adds.

Cost and Insurance Coverage

Despite the promising benefits of CGMs, many patients face obstacles in obtaining them because of their relative high cost. Medicare now covers CGMs for qualifying individuals, and some commercial health insurance plans cover them, too. But at this time, insurance coverage of CGMs varies greatly.

CGMs are more expensive than traditional finger-prick technology; Wharton says CGM technology costs users about $100 per month without insurance coverage. When the devices are covered by patients’ health insurance plans, they usually are covered at a rate of 80 percent as durable medical equipment rather than being treated as a pharmaceutical item. A few plans are offering coverage as part of pharmacy benefits.

Where to Buy CGMs

There are differences between the various brands and models of CGMs, especially as new and improved devices hit the market, but all require a physician’s prescription. Some CGMs even use implantable long-term sensors. A few common CGMs are listed below, though new products are continually being developed:

  • Freestyle Libre: This CGM is FDA-approved for people age 18 and up, does not require calibration, has a sensor life of 10 days, utilizes a handheld receiver, and is among the most affordable options currently. A newer model soon will be available with a sensor life of 14 days.
  • Dexcom G5 and G6: These models are FDA-approved for people age two and up, have sensor lives of 7-14 days (G5) and 10 days (G6), have customizable high/low alerts, and are considered a midrange price option. Results can be viewed on a reader device or can be set up to view on a smartphone or smartwatch.
  • Medtronic Guardian Connect: Among the newest models on the market, this CGM is FDA-approved for those ages 14-75, requires calibration 3-4 times daily, has a sensor life of seven days, communicates with a smartphone or smartwatch, and tends to be a more expensive device, with more variable coverage by insurance.

The Freestyle Libre can be purchased (with a prescription) at retail pharmacies such as Walgreens, CVS, and Walmart. The reader device costs about $65 without insurance, and the sensors (worn for 10-14 days, depending on the model) cost roughly $40 each. Online purchase options may be provided by the patient’s insurance plan. The Dexcom and Medtronic CGMs cannot currently be purchased at retail pharmacies, Wharton adds.

Wharton says she hopes more commercial insurance providers soon will expand their coverage of CGMs. At this time, the plans that do cover the devices generally only do so for patients with type 1 diabetes who are pregnant or who have significant problems with severely low blood sugar levels (usually under 50 mg). Guidelines for coverage under Medicare Part B are more inclusive in that the individual could have type 1 or type 2 diabetes as long as they are: 1) on three or more insulin injections per day; 2) testing their blood sugar at least four times a day to help adjust insulin dosing; and 3) seeing their treating physician at least twice a year.

In the near future at UAB Medicine, Wharton – along with fellow diabetes and nutrition education specialists Mariah Stewart, MS, RDN, LD, and Barbara Roberts, MS, RDN, CDE, LD – will begin providing consultation services to patients with diabetes who want hands-on training to learn how to use CGMs.

Click here to learn more about diabetes care at UAB Medicine, or call (205) 801-8711 to inquire about a referral to our Diabetes & Nutrition Education Clinic.